DESCRIPTION: Benzodiazepine agonists continue to be the principal pharmacologic option available for the treatment of anxiety, panic disorders, and insomnia. Despite an overall record of efficacy and safety that is generally favorable, concerns regarding tolerance, dependence, withdrawal syndromes, and abuse of benzodiazepines remain issues of medical and public health importance. Also of concern is the usage of these agents by the elderly, who may have increased susceptibility to adverse CNS depressant effects. There is continuing need for basic mechanistic data on the causes and consequences of tolerance and withdrawal; such data can form the basis for strategies to identify patients at highest risk, or to develop other pharmacologic interventions to minimize the risk of tolerance and dependence. We propose to continue and broaden our ongoing research program having this overall objective. The core of the model involves male CD-1 mice that receive continuous infusions of benzodiazepine agonists, or vehicle control, for up to 14 days via implanted osmotic pumps. During the period of infusion, and in the 7-day post-infusion withdrawal period, the following outcomes are determined: computerized ambulatory activity; pentylenetetrazole seizure threshold; in vivo benzodiazepine receptor occupancy; in vitro receptor binding; GABA(A) receptor function; receptor autoradiography; receptor subunit mRNA expression; and plasma and brain concentrations of infused substances. The principal research questions to be addressed include the following: a. Do benzodiazepine agonists with relative selectivity for the BZ1 receptor subtype have reduced liability to produce tolerance, dependence and withdrawal? b. Does the protein kinase C second messenger pathway have a modulatory role in benzodiazepine-associated tolerance? c. Does the excitatory amino acid (EAA) receptor system co-modulate the development of tolerance and withdrawal associated with benzodiazepine agonists, and does pharmacologic antagonism of specific EAA receptor systems modify these phenomena? d. Do aging organisms have differential patterns of benzodiazepine tolerance and withdrawal? Are such differences explained by protein kinase C or EAA regulatory systems? These studies should continue to provide mechanistic data relevant to the clinical management and prevention of tolerance and dependence problems associated with therapeutic use of benzodiazepine agonists.